Thursday, April 26, 2018

Progress In Determining The Standard Model Neutrino Parameters

In the Standard Model, there are seven experimentally determined constants pertaining to neutrinos - the three neutrino masses and the four parameters of the PMNS matrix that governs neutrino oscillations. Progress has been made recently in determining some of those parameters:

We present an up-to-date global analysis of data coming from neutrino oscillation and non-oscillation experiments, as available in April 2018, within the standard framework including three massive and mixed neutrinos. We discuss in detail the status of the three-neutrino (3nu) mass-mixing parameters, both known and unknown. Concerning the latter, we find that:

In addition, the differences between the masses of the three neutrino masses are all known to reasonable accuracy, and that combined with the lower bound that none of the neutrino masses can be less than zero, and the upper bounds provided by cosmic background radiation experiments, actually places moderately strong limitations on each of the possible absolute neutrino masses, although all are known only to order of magnitude precision.

5 comments:

"In addition, the differences between the masses of the three neutrino masses are all known to reasonable accuracy, and that combined with the lower bound that none of the neutrino masses can be less than zero, and the upper bounds provided by cosmic background radiation experiments, actually places moderately strong limitations on each of the possible absolute neutrino masses, although all are known only to order of magnitude precision."

what is the current estimated values for neutrino masses and differences between the masses of the three neutrino masses?

"The sum of the neutrino masses in an inverted hierarchy, we know from neutrino oscillation data, cannot be less than 98.6 meV. In a normal hierarchy, the sum of the neutrino masses must be at least a bit more than 65.34 meV. A global look at various kinds of astronomy data suggests that there is a 95% chance that the sum of the three neutrino masses is, in fact, 90 meV or less. This strongly favors a "normal hierarchy" of neutrino masses.

The state of the art measurements of the difference between the first and second neutrino mass eigenstate is roughly 8.66 +/- 0.12 meV, and the difference between the second and third neutrino mass eigenstate is roughly 49.5 +/- 0.5 meV, which implies that the sum of the three neutrino mass eigenstates cannot be less than about 65.34 meV with 95% confidence.

So, this also gives us absolute neutrino mass estimates that have relative precision comparable to that of the experimental value of lighter quark masses and precision in absolute terms that is truly remarkable. It narrows the range of each of the neutrino masses to a nearly perfectly correlated window only a bit larger than +/- 4 meV. This is a roughly 33% improvement over the previous state of the art precision with which the absolute neutrino masses can be estimated.

The bottom line is that the range of the three neutrino masses that would be consistent with experimental data is approximately as follows (with the location of each mass within the range being highly correlated with the other two and the sum):

Mv1 0-7.6 meVMv2 8.42-16.1 meVMv3 56.92-66.2 meV

Sum of all three neutrino masses should be in the range: 65.34-90 meV."

It is not that clear from Table 1 that the mass sum should be so far above 0.06eV. Anyway, good to see CP coming out near maximal and nor al ordering slowly being pinned down. Exciting times, and a lot of work to do!